Hood for therapeutic lamps



Aug. 11, 1931. Y F. BIRD ,5

-HOOD FOR THERAPEUTIC LAMPS Filed July 26,-1930 I BY Java-[26R V ATTORNEY Patented Aug. 11, 1931 UNITED STATES PATENT. OFFICE LESTER'F. BIRD, DIE-NEWARK, NEW JERSEY, ASSIGNORTO HANOVIA CHEMICAL. AND. MANUFACTURING COMPANY, or NEWARK, NEW JERSEVYKA CORPORATION OF NEW JERSEY Application filed July 26,

This invention refers to hoods and reflectors for therapeutic lamps of any character and especially to those known as mercury arc lamps.

There are certain features in connection with the use of mercury arc "lamps that make this invention of peculiar value. Theuse of mercury arc-lamps is increasing steadily since they are a very eflicient source of ultraviolet light and are active in that region of the spectrum that has been shown to be effective in the production of sunburn.

It is highly desirable that patients who are exposed to the rays from these lamps be given the maximum amount of light in the shortest possible time.

The light given out from an open burner without the use of a modifier-or reflector is not suitable for the maximum results be"- cause of its distribution. -The open burner I acts substantially as a point source of light 30 and so is'more intense close to the burner than farther away. 7

Because of the speed of treatment-that is desired the patients are placed as close to I the lamp as the distribution of the light will permit.

If the patient is 'far away from the open lamp he will receive practically uniform illuminationbut at the distances ordinarily employed for this purpose,

this is not the case. 4'0

The usual treatment method is to place the patient in a prone position beneath the burner at a distance of L-to 6 feet. WVit-h this distance from the burner for treatments, the light falling on the] part of the patient directly beneath the burner is very much more intense than "that on the extremities, in fact-it may easily amount to twice the intensity of that on the extremities.

Such conditions as these make some form 0f modifier or reflector a necessityif' the HOOD FOR THERAPEUTIC LAMPS 1930. semi No. 470,950.

maximum results aresecured from the lamp.

The object of this invention is to provide a modifier by means of which substantially uniform illumination is obtained below the burner in the place normally occupied by the patient, thus enablingthe maximum benefit from a lamp. The efficiency of the light source is also greatly increased since almost all of'the light from the burner is converted into useful light.

Light is returned from all directions and is directed downward so thatfit becomes useful for the patient. The reflecting surfaces are composed of polished surfaces of those metals such as chromium and aluminum which have been found to be the most efficient in the reflection of ultraviolet light.

A further objectis the provision of a modifier for the light so that the light in those places about the lamp thatnormally receive weakened radiation are strengthened, and those that would be too strong are weakened. The reflector provides'a strong light field for the patients head and feet but does not appreciably affect the mid-section.

The mercury arc burner which produces the light is usually a quartz tube about 4 inch in diameter and 5 inches long. This envelope contains only mercury and mercury vapor. Under the proper conditions the burner may be connected to a power source of electricity and an are established within the quartz tube. v

The arc in the burner fills the quartz containerfrom one end to the other and so is in itself a distributed source of light. This physical shape of the light source requires a reflector differing radically from those ordinarily employed with concentrated filament 'rlam-ps.

invention takes this condition into account and the reflector is "so designed that the greatest possible use is made of the distribution of the light source.

These and other advantageous objects, which will later appear, are accomplished by the's-i m' ple and practical construction and] arrangement "of parts hereinafter described and exhibited in the accompanying drawings, forming part hereof, and in which:

Figure 1 represents an end view of the device, with a portion of an end plate re moved.

Figure 2 represents a view taken on line 22 of Figure 1.

Figure 3 represents a diagram illustrating the intensities of light necessary to produce uniform illumination of a flat surface.

Referring to the drawings, the reflecting hood is shown to include a plurality of metal plates 4, of varying sizes, each plate having lateral flanges 4 and end flanges 6. The plates are made from metals, such as chromium and aluminum, which may be highly polished so that the interior faces of the plates may have high reflecting powers for ultraviolet radiations.

End plates 5 are attached to the reflecting plates 4 by means of bolts 7 passing through the flanges 6. The end plates 5 are provided with flanges 5. Immediately behind the light source 9, a reflecting plate is omitted to provide a space 8 for ventilating purposes. The space 8 is one inch in length. The plates 4 are arcuately arranged and both sides of the hood are symmetrical, the plates on one side of the hood being inclined successively to the flange 5-5 at angles of 49 44, 25 ,4 2 and 7, said plates having respectively widths of 125/32 inches, 3-9/32 inches, 1-57/64 inches and 23/32 inch, the plates on both sides of the hood being arranged in identically the same manner.

According to the well known laws of light distribution the energy falling on a. given perpendicular surface varies with the distance of the light source from the surface. That is, if a surface is one foot from a given light source it will have a larger amount of light energy falling upon it than it will at a distance of two feet or more from the lamp. The energy, if from a point source, will vary approximately inversely as the square of the distance. If the distance is increased the light energy is reduced. If the distance is decreased, the light energy is increased.

Where uniform light intensity is desired upon a given surface, as is the case when a patient is receiving a treatment from a lamp, since the patient represents a rela-.

tively fiat straight surface, considerable modification of the light distribution is necessary to obtain uniform intensity.

With the unmodified burner and a patient four feet directly under the lamp the distance from theburner is considerably greater from the patients head and feet than from mid-section. Such distribution results in a considerable increase in the light re- I ceived by the mid-section as compared to that secured by the head and feet.

The distribution of the light from an unmodified light source such as the mercury are is practically uniform around the burner. lVhen the burner is mounted four feet above a patient who is six feet long the mid-section of the patient is four feet from the burner while his head and feet are all of five feet away from the lamp.

As stated before, the light at his head and feet will be considerably weaker than at the mid-section and this will be approximately inversely as the square of the distance. Since one distance is four and the other distance five, the corresponding intensities will be approximately as sixteen is to twentyfive, that is, the light at the patients feet and head will be only 16/25th as strong as that at the mid-section.

There is still another condition that results in the weakening of the light at the patients head and feet over the light at the mid-section and that is the angle at which the light strikes the surface. The smaller the angle at which the light strikes the surface, the lower the intensity per unit area on the surface. For example, a surface of ten square inches in a plane surface, at right angles to the light, would receive the maximum light.

If it were edge on to the light there would be no light striking the surface, and for an intermediate angle there would be less light striking the surface than would be the case when it is at right angles to the light. Under the conditions given previously with the are four feet above the patient and the patient six feet long, the angle at which the light hits the patients head and feet is such that the intensity per unit area is reduced to about four-fifths of the intensity that would be secured by a surface at right angles to the light at the same location.

In the design of the modifier both the angle of incidence of the light and the distance from the light source must be taken into account.

Starting with the mid-section of the patient and proceeding toward the head the light distribution should follow a regularly increasing curve as illustrated in Figure 3.

The reflector adds greatly to the efliciency of the light source because it redirects light that normally would be wasted so that it is available on the patient. No reflector is 100 per cent efficient as a reflector and does not reflect all of the light it receives. Some of the light is absorbed and some is scattered so that it is lost.

Reflectors are available however that will reflect in a useful direction about 50 percent of the incident light. The increase in intensity that is possible with a reflector of the proper design is a matter of common knowledge. Ordinary designs of reflectors are not suitable for the purpose for which this invention was made.

The reasons for this are apparent when the source of the light and the desired distribution are considered. Thelight source is not a concentrated filament as is common in incandescent lamps but is a cylindrical tube about five inches in length. The light intensity throughout the length of the tube is about constant so that the light source is distributed itself.

This fact influences the design of the reflector. It is common practice with reflectors to design them so that the light is brought to a focus giving a ver concentrated spot of high intensity. uch distribution is not desirable for a therapeutic lamp which is used for irradiation of a patient.

Such distribution would result very un-' favorably since the patient might receive too much light in one place and very much less in another. The light striking the patient should be of uniform strength throughout.

Another very important advantage is secured from the invention because of the peculiar and inherent characteristics of a quartz mercury arc lamp. These arcs are affected markedly by the temperature of the surrounding envelope and the temperature of the envelope is in turn affected by many external conditions such as ventilation, air

temperature and radiation. The air temperature in the room Where the lamps are located while of importance to the burner is however not within the control of the burner and hood designer.

The temperature of the air immediately surrounding the burner, the ventilation of the hood, the radiation of heat from the burner and the distribution of the light from the burner are all more or less under the control of the designer.

Hoods and reflectors that are improperly designed cause high temperatures to exist in the air around the burner. This does not damage the burner but does reduce the eiflr ciency and the light output from it.

The input power to the burner is aflected and reduced by a rise in temperature of the burner envelope and this in turn causes a reduction in the output from the lamp.

Proper ventilation of the hood is of considerable importance in securing the maximum output from a given burner. There can easily exist a loss in output from a burner of 30 percent by placing the burner in a location having poor ventilation.

Another important consideration in the hood design is that of properly directing the radiation given off from the burner. Improperly designed hoods reflect the radiations directly back into the burner and so add to its temperature. This of course results in reduced light output and is undesirable.

The quartz mercury arc is quite opaque to the radiations that it emits so there is no gain in intensity by tr ing to reflect light through the burner. itselfl tions toward the burner.

The invention successfully cares for all of these important considerations. A maximum of ventilation is provided for the burn er and the natural draft associated with the burner provides a continuous flow of cool air to the burner at all times. The hood for this reason does not interfere in any way with the burner temperature and so provides for the coolest possible operating conditions.

,The surfaces of the reflector, while intended for excellent distribution of light to the patient who might be enjoying the radiations from the lamp, are arranged so that there is no reflected radiation striking the burner. This is a great advantage since the burner is kept cooler and at a higher efliciency.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent, is:

In combination with a therapeutic mercury vapor arc lamp, a reflecting hood comprising a pair of end plates, and a plurality of plane reflecting surfaces attached to the end plates, and arcuately arranged, the plates on one side of the hood being inclined successively to the longitudinal free edge of the hood at angles of 49 4 F 25 16, and 7, and said plates having respectively widths of 1-25/32 inches, 3-9/32 inches, 167/64 inches .and 23/32 inch, the plates on the other side of the hood being arranged in identically the same manner, the adjacent plates of each side being spaced apart, a distance of one inch, the light source being positioned on a line through the center of the hood at a distance of 2 inches from the longitudinal free edge.

This specification signed this 21st day of July, 1930.

LESTER F. BIRD.

It is advantage-V ous that a reflector doesnotreflect any radia- 

